rear toe in greatly affects the steering of the car, it depends whether or not your on power or off power.
like i said, i dont have the answer to your problem, but if you do some testing , im sure you will be bale to notice the difference when you make your changes.
for example, adjust your castor so its maxxed out, then try a few laps, see what the car does, then try it the opposite way and see what it does.
i would say that if your car is oversteering out of a turn, then try more toe in on the rear.
dont go more than 5 degrees, if it doesnt do what you want then go to 1 or 2 degrees of toe in, then see what happens.im not an expert at set-up, i dont know anyone that is, its mainly trial and error that usually works the best.
good luck!